This invention relates to an apparatus for building pneumatic tires and particularly radial cord type tires. Pneumatic tires and particularly bias type pneumatic tires have been generally built in a flat annular band and subsequently expanded to the toric shape while being cured in a mold. Illustrative of the art generally are the equipment and methods described in U.S. Pat. Nos. 2,614,951, 2,614,052, 3,171,769, 3,156,601 and 3,645,826, which are owned by the assignee of the present application. Pneumatic tires of the radial type, on the other hand, have been commercially built by the "toric match" method where the tire carcass is assembled in a flat annular band and then expanded to a toric shape in order to apply a separately formed tread and belt assembly. Such equipment for making radial type tires is described and claimed in U.S. Pat. No. 3,475,254, which is also owned by the assignee of the present application.
In a typical radial tire, cords in the carcass plies extend from bead portio to bead portion in a direction substantially perpendicular to the circumferential centerline of the tire. The cords in the belt strips typically extend across the same circumferential centerline at a small angle (i.e., 20.degree. or less). As a result, belt assemblies used in radial tire construction are radially substantially inextensible. For this reason, the carcass of the tire on the one hand and the tread and belt assembly on the other are typically assembled in separate flat annular bands of different diameter. Thereafter, it is necessary that the tire carcass be expanded to a toric shape approximating its final diameter before applying the separately built tread and belt assembly.
Non-uniform or asymmetric toric expansion of the tire carcass can cause structural imperfections in the resulting tire. For example, the tire carcass or the carcass building drum shaping bladder, or both, may have surface eccentricities or imperfections. These imperfections are accentuated during the toric expansion of the carcass and can cause the tire carcass and the tread and belt assembly to mate irregularly and in misalignment. The resulting pneumatic tire thus possesses irregularities which can adversely effect the tire's overall performance.
Attempts have been made to provide annular guides for use in shaping the carcass during its radial expansion into toric shape. For example, tire building drums with such carcass shaping guides are disclosed in U.S. Pat. Nos. 3,047,450, 3,184,361, 3,434,987 and 3,740,292. A principal disadvantage of these types of annular guides, however, is that they produce frictional engagement between the guides and the tire carcass. This sliding friction can result in uneven and irregular expansion.
The present invention substantially reduces or eliminates such difficulties and disadvantages in the toric mating of a radial type tire carcass with a tread and belt assembly. It provides a means by which the tire carcass is mated with the tread and belt assembly substantially regularly, uniformly and, when desired, symmetrically.
The equipment in association with which the present invention is used is adapted to make radial type pneumatic tires by a technique that includes building a tire carcass on a carcass building and shaping drum rotatably mounted on a shaft. A rubberized cord ply or plies are disposed around the building drum to form an annular carcass band with edge portions over-hanging the ends of the drum. Bead portions are then formed in the carcass band preferably by forming bead ring receiving shoulders at the ends of the drum, and setting or abutting separately assembled annular bead rings at the formed bead ring receiving shoulders. The bead portions are completed by utilizing turnover means which wrap edge portions of the ply or plies around the bead rings where the edge portions are stitched to the outer surface of the carcass band. Other components such as sidewall assemblies, chafer strips, etc., can then be applied to complete the tire carcass.
Thereafter, transfer means grip a tread and belt assembly and position said assembly circumferentially around and precision spaced from the tire carcass, in precision alignment relative to the tire carcass, symmetrically or asymmetrically of the circumferential centerline of the tire carcass as desired. Typically, for radial type tires, the tread and belt assembly includes inextensible belts of spaced, substantially rubberized parallel cords overlayed with a suitable tread rubber annulus. The tread and belt assembly is usually separately assembled on a second building drum and transported by transfer means into concentric position in a manner similar to that described in the above-mentioned U.S. Pat. No. 3,475,254.